If you’re doing any teaching online you need be aware of the copyright rules.
If you work in education in Australia the best place to go is the SmartCopying site. It’s been set up by the National Copyright Unit which provides the guidelines for Australian Schools and TAFE. It’s pretty safe to say it applies to universities too.
As a teacher you should be covered by a Statutory Education Licence which gives you a fair bit of protection and flexibility around copying images and resources and using them within your organisation. But if you’re in a Private college or RTO it would be worth checking the list on the site to see if you’re licenced.
It has a section on Creative Commons licencing which is probably the safest place to go for free images. CC is not foolproof. People can add a CC licence to images they don’t own, and there have been cases of people harvesting free CC images and selling them to commercial platforms, who have in turn sent cease and desist letters to legitimate users.
If you’re not sure about an image check it with TinEye.
If you’re commercial operator creating resources or delivering online courses then the Statutory Education Licence rules don’t apply. You need to follow the commercial guidelines – which basically means use your own images or pay for someone else’s. I see quite a few people who transition from schools to the commercial sector get tripped up by this.
For free images Creative Commons is the safest place to go, but always check the licence tags. Quite a lot are tagged “not for commercial use”.